Download Force and Newton`s First Law

Physics
the study of the relationship between
matter and energy
Motion

A change in position in a certain amount of
time

Motion is relative. To know you are
moving, you must have a reference point

Distance – how far you traveled
Distance vs. Displacement

The distance between the final position and
starting position is displacement

(Ex: hiking on a trail. The trail may be 1 mile
long but you may only end up 300 ft from where
you started)
Speed Equation
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Speed – the distance traveled divided by the
time needed to travel that distance
SI Unit is meters per second (m/s)
Speed = distance
time
D
S
T
Practice
(Make sure you use the proper units)

If it takes you 3 hours to travel 60 miles, what
is your speed??

If you are running 3 miles in 30 minutes, what
is your speed?
Constant speed vs. Average speed

Constant speed – an object covers equal
distances in equal amounts of time

The speed of moving objects is not always
constant

Average speed: total distance
total time
Graphing Speed
What is happening in the following graph?
Velocity

Velocity: Speed in a given direction

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You can be going the same speed but two
different velocities
Velocity = distance + direction
time
D
V
T
Acceleration

The change in velocity divided by the time the
change occurs
A = Velocity(final) – Velocity(initial)
Time

Acceleration is speeding up, slowing down or
changing direction
Stop Here!!!
Force

What causes an object to accelerate?

A force is a push or pull exerted on an object

Force is measured in Newtons (kg m/s2)

In order for an object to speed up, slow down or change
direction, a force has to act on that object

Inertia is the object’s tendency to resist changing its
motion. The more inertia, the harder it is to start moving
or slow it down
Total Force

Sometimes, more than one force can act on an object
at the same time. Those forces together will affect
the object’s motion.

Forces usually act in pairs with one force
acting on either side of the object

The resulting force that exists between
two is the total force
Unbalanced Forces
When a total force acts on an object, they are
said to be unbalanced.
Unbalanced forces can cause an object to start
moving, stop moving, or change direction.
Balanced Forces

Balanced forces exist when the total force is
equal to zero.

Balanced forces do not change an object’s
motion
Friction and Air Resistance

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Friction is the force between two objects
in contact that resists motion between
two touching surfaces
It is what eventually causes things to
slow down and stop
Air Resistance is a form of friction
between an object and air molecules
Gravity


Gravity is the pull that all matter exerts on other
matter
Gravity is dependent on the mass of an object and
the distance between the two objects



The greater the mass, the more gravitational pull it will
have (i.e.: earth vs. moon)
The greater the distance, the less gravitational pull it will
have
Mass vs Weight – weight is the amount of
gravitational pull on a person. So on the moon, your
mass would be the same but weight would be
different
Free Fall and Terminal Velocity

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When the only force acting on an object is
gravity, the object is said to be in free fall
On earth, this is 9.8 m/s2 - Gravity constant
In the absence of air resistance, all objects on
Earth accelerate at the same rate, regardless of
their mass.
An object reaches its terminal velocity when
the force of gravity is balanced by the force of
air resistance
Gravity Demo
Newton’s Laws
Newton’s First Law of Motion

“An object at rest will remain at rest and an

object in motion will maintain its velocity
unless it experiences an unbalanced force.”
This is often times called the law of Inertia
Newton’s Second Law of Motion

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“The unbalanced force acting on an object
equals the object’s mass times its
acceleration”
F=ma
Force is measured in Newtons (kg m/s2)
Newton’s Third Law

For every action force, there is an equal and
opposite reaction force